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Table 7. Modified Wentworth Particle Size Scale. <br /> Approx. <br /> Range Median <br /> (mm) (mm) <br /> <br />Mamouth Boulder 4000 - <br />Very Large Boulder 3500 - 4000 3750 <br /> 3000 - 3500 3250 <br /> 2500 - 3000 2750 <br /> 2000 - 2500 2250 <br />Large Boulder 1650 - 2000 1825 <br /> 1330 - 1550 1490 <br /> 1000 - 1330 1165 <br />Medium Boulder 830 - 1000 915 <br /> 665 - 830 750 <br /> 500 - 665 580 <br />Small Boulder 415 - 500 450 <br /> 335 = 415 375 <br /> 250 - 335 290 <br />Large Cobble 190 - 250 220 <br /> 130 - 190 160 <br />Small- Cobble 100 - 130 17.5 <br /> 64 - 100 85 <br />Very Course Gravel 50 - 64 57 <br /> 32.- 50 40 <br />Coarse Gravel 16 - 32 24 <br />Medium Gravel 8 - 16 12 <br />Fine Gravel 4 - 8 6 <br />Pea Gravel 2 - 4 3 <br />Very Coarse Sand 1 - 2 1.5 <br />Sand .062 - 1 .5 <br />Silt-Clay •062 -- <br />(o `1